Spontaneous symmetry-breaking in optomechanical cavity

A theoretical consideration of the so-called "membrane-in-the-middle" optomechanical cavity revealed that it undergoes a spontaneous symmetry breaking as a function of the transparency of the membrane. Such typical features of this phenomenon as a square-root development of the order parameter and divergency of the critical susceptibility were identified. In the contract to classical spontaneous-symmetry-breaking systems of ferromagnets and ferroelectrics, in the considered system, this divergency remains, due to interference effects, an "internal" property of the system, which does not reveal itself in any divergency of its observables. A spontaneous symmetry breaking in an optomechanical cavity might pave a new way to enhanced optomechanical interactions

Dynamic flexoelectric effect in perovskites from first principles calculations

Using the dynamical matrix of a crystal obtained from ab initio calculations, we have evaluated for the first time the strength of the dynamic flexoelectric effect and found it comparable to that of the static bulk flexoelectric effect, in agreement with earlier order-of-magnitude estimates. We also proposed a method of evaluation of these effects directly from the simulated phonon spectra. This method can also be applied to the analysis of the experimental phonon spectra, being currently the only one enabling experimental characterization of the static bulk flexoelectric effect

Impact of surface phenomena on direct bulk flexoelectric effect in finite samples

In the framework of a continuum theory, it is shown that the direct flexoelectric response of a finite sample essentially depends on the surface polarization energy, even in the thermodynamic limit where the body size tends to infinity. It is found that a modification of the surface energy can lead to a change of the polarization response by a factor of two. The origin of the effect is an electric field produced by surface dipoles induced by the strain gradient. The unexpected sensitivity of the polarization response to the surface energy in the thermodynamic limit is conditioned by the fact that the moments of the surface dipoles may scale as the body size

Optical mode crossings and the low temperature anomalies of SrTiO3

Optical mode crossing is not a plausible explanation for the new broad Brillouin doublet nor for the strong acoustic anomalies observed at low temperatures in SrTiO3. Data presented to support that explanation are also inconclusive.Comment: This is a comment to a paper from J.F. Scott (same ZFP volume

Bichiral structure of feroelectric domain wall driven by flexoelectricity

The influence of flexoelectric coupling on the internal structure of neutral domain walls in tetragonal phase of perovskite ferroelectrics is studied. The effect is shown to lower the symmetry of 180-degree walls which are oblique with respect to the cubic crystallographic axes, while {100} and {110} walls stay "untouched". Being of the Ising type in the absence of the flexoelectric interaction, the oblique domain walls acquire a new polarization component with a structure qualitatively different from the classical Bloch-wall structure. In contrast to the Bloch-type walls, where the polarization vector draws a helix on passing from one domain to the other, in the flexoeffect-affected wall, the polarization rotates in opposite directions on the two sides of the wall and passes through zero in its center. Since the resulting polarization profile is invariant upon inversion with respect to the wall center it does not brake the wall symmetry in contrast to the classical Bloch-type walls. The flexoelectric coupling lower the domain wall energy and gives rise to its additional anisotropy that is comparable to that conditioned by the elastic anisotropy. The atomic orderof- magnitude estimates shows that the new polarization component P2 may be comparable with spontaneous polarization Ps, thus suggesting that, in general, the flexoelectric coupling should be mandatory included in domain wall simulations in ferroelectrics. Calculations performed for barium titanate yields the maximal value of the P2, which is much smaller than that of the spontaneous polarization. This smallness is attributed to an anomalously small value of a component of the "strain-polarization" elecrostictive tensor in this material